The invention relates to a device for measuring the flash point of liquids and solids in a measurement chamber, which is formed by a measurement basin and a lid and which is provided with means for heating the liquid or the solid in the measurement basin, an electrical igniter having a spark gap, temperature sensors, a pressure measuring apparatus, and a press-on device for tightly connecting the measurement basin and the lid, a control device also being provided in order to control the heating means, the igniter and the press-on device and to collect the measured values of the temperature sensors and of the pressure measuring apparatus.
Such a device has become known for example from EP 486 980 B1. The flash point of a liquid or of a solid is ascertained in such a way that the substance to be investigated is first put into a heatable measurement chamber, and the ascertainment of a flame generation, which is carried out in order to determine the flash point, takes place by measuring the pressure present in the measurement chamber after an ignition, said pressure increasing when the substance to be investigated ignites as a result of the temperature increase brought about by the flame in the measurement chamber.
The flash point of a substance is used in transport and safety regulations in order to define inflammable and explosive materials and to provide information concerning the presence of highly volatile and flammable components in a low-volatility and non-flammable substance.
According to ASTM, the flash point is defined as the lowest temperature, corrected to a barometric air pressure of 101.3 kPa, at which the vapour of the sample ignites as a result of the application of a test flame, wherein a flame arises which itself wanders over the surface of the sample and covers at least two thirds of the surface.
The flash point of a substance is ascertained under laboratory conditions with exposure to air.
A number of measurement methods recognised by the ASTM and ISO exist worldwide for measuring the flash point. Use is always made of a sample vessel, which is heated by flame or electrically. The open sample vessel is hardly any longer admissible for test measurements, since the highly volatile components evaporate and can no longer contribute to the combustion.
In the case of the method known from EP 486 980 B1, the procedure is such that the substance to be measured, mainly a liquid, is filled into the measurement basin in a predetermined quantity. The measurement basin is pressed against the heatable lid either manually or automatically.
The measurement procedure is started by the lid being heated to a predetermined temperature which is reliably below the expected flash point temperature. The monitoring and measurement of the temperature takes place by means of a temperature sensor.
As a result of the temperature contact of the measurement basin with the lid, the basin is also heated. However, its temperature remains below the temperature of the lid.
After a waiting time for the temperature equalisation of the measurement basin and the lid, the temperature of the lid is slowly increased further and an ignition by means of electrodes is carried out at constant temperature intervals. Immediately after the ignition, the rise in pressure is measured in the measurement chamber by means of a pressure measuring apparatus, which is preferably constituted as a piezoresistive pressure sensor. The flash point temperature is indicated by a further temperature sensor. The measurement chamber is defined by the measurement vessel or the volume of the substance to be measured and the free space under the lid.